Coating compositions employing zinc antimonate anhydride particles

ABSTRACT

The invention relates to coating compositions employing zinc antimonate anhydride comprising zinc antimonate anhydride particles and a liquid of a part-hydrolyzed silane coupling agent, a liquid of hydrolyzed ethylsilicate, a liquid of hydrolyzed methylsilicate, or a resin emulsion. The zinc antimonate anhydride particle having a ZnO/Sb 2  O 5  molar ratio in a range of from 0.8 to 1.2, a crystal structure of zinc antimonate anhydride (Zn Sb 2  0 5 ), and a primary particle size in a range of from 5 to 500 nm. The particle production method comprises the steps of mixing a zinc compound with a colloidal antimony oxide at a ZnO/Sb 2  O 5  molar rate in a range of from 0.8 to 1.2, followed by calcining the mixture within a temperature range of from 500 to 1100° C. The particles are applicable as a flame retardant for plastics, a smoke suppressant, antistatic agent for plastics and glasses, and resistor.

This is a Division of application Ser. No. 08/711,460 filed Sep. 11,1996, now U.S. Pat. No. 5,707,552, which in turn is a Division ofapplication Ser. No. 08/254,708 filed Jun. 6, 1994, now abandoned.

BACKGROUND

The present invention relates to a particle having a molar ratio ofZnO/Sb₂ O₅ in a range of from 0.8 to 1.2, having a crystal structure ofzinc antimonate anhydride (ZnSb₂ O₆) and a primary particle size in therange of from 5 to 500 nm, and to a sol of these particles and a methodfor producing these particles and sol. The particle of the presentinvention is used in a variety of applications such as flame retardantsfor plastics, smoke suppressants, antistatic agents for plastics andglass, and resistors.

Acta Chemica Scandinavia, A, Vol. 29, pp. 803-809 (1975) discloses azinc antimonate (ZnSb₂ O₆) prepared by heating zinc oxide and diantimonytrioxide to 800° C. at a time scale of 4 hours to 3 weeks, bypulverizing the heated mixture, annealing the pulverized mixture at atemperature ranging from 900 to 1,000° C. at a time scale of 4 hours to2 weeks, and gradually cooling the annealed mixture to room temperature.Zeitschrift fuer Kristallographie, Vol. 98, pp. 185-190 1937 presentsobservation data of X-ray diffraction of zinc antimonate anhydride{Zn(SbO₃)₂ }. American Mineralogist, Vol. 40, pp 64-69 (1955), andGeological Society of America Memoir, Vol. 85, pp. 209 (1962) presentobservation data of X-ray diffraction of zinc antimonate anhydride(ZnSb₂ O₆, Ordonezite).

JP-A-3-267143 (the term "JP-A-" referred to hereinafter signifies"unexamined Japanese patent publication") discloses a compositionconsisting of zinc oxide and diantimony pentoxide which was prepared bymixing an acidic aqueous sol of diantimony pentoxide and basic zinccarbonate at a molar ratio of ZnO/Sb₂ O₅ in a range of from 0.5 to 10 toform a uniformly dispersed slurry, performing decarbonation of the basiczinc carbonate in the slurry at a temperature range of from 50 to 100°C. to a molar ratio of CO₃ /ZnO in a range of from 1/5 to 1/500, and bydrying the slurry in a temperature range of from 150 to 250° C.

The method disclosed in Acta Chemica Scandinavia described aboveproduces zinc antimonate anhydride by mixing zinc oxide and diantimonytrioxide and by calcining the mixture. The particle size of the obtainedzinc antimonate anhydride is, however, not given in the description.Since ordinary diantimony trioxide has a large primary particle size,the primary particle size of zinc antimonate anhydride obtained by thismethod is 500 nm or more. Accordingly, when particles of this type areused as a flame retardant or smoke suppressant, they do not provide acompletely satisfactory effect. In addition, particles of this type havethe disadvantage of not providing a sol even by pulverizing, because oftheir large primary particle size. The method disclosed in JP-A-3-267143employs a low calcining temperature so that the product has a primaryparticle size of 500 nm or less. Nevertheless, X-ray diffractionmeasurement shows a peak of diantimony pentoxide and not a peak of zincantimonate anhydride. Consequently, the product thereof is not zincantimonate anhydride.

The present invention provides a particle having a molar ratio ofZnO/Sb₂ O₅ in a range of from 0.8 to 1.2, a crystal structure of zincantimonate anhydride (ZnSb₂ O₆) and a primary particle size in the rangeof from 5 to 500 nm, relates to a sol of these particles and a methodfor producing these particles and their sol.

SUMMARY

The particle of the present invention has a molar ratio of ZnO/Sb₂ O₅ inthe range of from 0.8 to 1.2, a crystal structure of zinc antimonateanhydride (ZnSb₂ O₆), and a primary particle size in the range of from 5to 500 nm.

The production method of the particles of the present invention ischaracterized by mixing a zinc oxide and a colloidal antimony oxide at amolar ratio of ZnO/Sb₂ O₅ in a range of from 0.8 to 1.2, followed bycalcining the mixture in a temperature range of from 500 to 1,100° C.

According to the production method of the particles of the presentinvention, when the colloidal antimony oxide is an antimony oxide sol,it is mixed with a zinc compound, and the mixture is dried and calcinedat a temperature ranging from 500 to 1,100° C. to obtain the requiredparticles.

The zinc compound used in the present invention is one zinc compound ormore selected from a group of zinc hydroxide, zinc oxide, a zinc salt ofinorganic acid, and a zinc salt of organic acid.

Examples of a zinc salt of inorganic acid are zinc carbonate, basic zinccarbonate, zinc nitrate, basic zinc nitrate, zinc chloride, basic zincchloride, zinc sulfate, and basic zinc sulfate. Examples of a zinc saltof organic acid are zinc formate, zinc acetate, zinc oxalate, and basiczinc oxalate. These zinc compounds are available as commerciallyavailable industrial chemicals. However, when zinc hydroxide or zincoxide is used, it is preferable to use those having a primary particlesize of 500 nm or less, and to use zinc hydroxide powder, zinc oxidepowder, zinc hydroxide sol or zinc oxide sol having a particle size inthe colloidal range. It is more preferable still to use a salt having anacid radical which volatilizes during calcining, a carbonate, a nitrateor a salt of organic acid. Those compounds may be used in an alone or amixture.

The colloidal antimony oxide used in the present invention has a primaryparticle size of 300 nm or less, and examples of a compound thereof arediantimony pentoxide sol, hexantimony tridecoxide sol, diantimonytetroxide hydrate sol, and colloidal diantimony trioxide. Diantimonypentoxide sol may be prepared by a known method, including a method foroxidizing diantimony trioxide (disclosed in JP-B-57-11848) (the term"JP-B-" referred to hereinafter signifies "Examined Japanese PatentPublication"), a method of de-alkalizing alkali metal antimonate bymeans of an ion exchange resin (disclosed in U.S. Pat. No. 4,110,247),and a method for treating sodium antimonate by means of an acid(disclosed in JP-A-60-41536, JP-A-62-182116). Hexantimony tridecoxidesol may be prepared by a method for oxidizing diantimony trioxide(disclosed in JP-A-62-125849), and diantimony tetroxide hydrate may alsobe prepared by a method for oxidizing diantimony trioxide (disclosed inJP-A-52-21298). Colloidal diantimony trioxide may be produced by a vaporphase process (disclosed in JP-B-61-3292). The antimony oxide sol usedin this invention preferably has a primary particle size ranging from 2to 200 nm and is preferably an acidic sol containing no base such assodium or amine. Antimony oxide sol may use that which contains anantimony oxide (Sb₂ O₅, Sb₆ O₁₃, or Sb₂ O₄) at a concentration of from 1to 60 wt. %, and the sol may be dried by a vacuum drying method or afreeze drying method to be used as a dried product of antimony oxidesol. The colloidal antimony oxide is available as a commercialindustrial chemical in a form of diantimony pentoxide sol, diantimonypentoxide powder or diantimony trioxide ultrafine powder.

Mixing of the above-described zinc compound and antimony oxide sol maybe conducted in a temperature range of from 0 to 100° C. for a mixingtime ranging from 0.1 to 30 hours using a Satake agitator, Pfaudleragitator, disper mill, or the like. Mixing of the zinc compound with thedried antimony oxide sol or the colloidal diantimony trioxide may beperformed using a mortar, a V-shape mixer, a Henschel mixer, a ball millor the like.

In the present invention, it is preferable to mix the zinc compound withthe antimony oxide sol or a dried product thereof, or with the colloidaldiantimony trioxide at a molar ratio of ZnO/Sb₂ O₅ in a range of from0.8 to 1.2. According to the present invention, the drying procedure ofthe above-described mixture (slurry) of zinc compound and antimony oxidesol may be performed at 500° C. or below using a spray drier, a drumdrier, a box hot air circulation drier, a vacuum drier, or a freezedrier. Also, the slurry may be dried by separating the cake using asuction filtration unit, a centrifugal filtration unit or a filterpress, or further by removing soluble impurities (such as SO₄, which ishard to volatilize during calcining) by pouring a pure water from thestarting materials at need to form a wet cake, and by drying the cakewithin a temperature range of from room temperature to 500° C. using abox drier or other type of drier described above. The drying procedureis preferably conducted at 300° C. or below in consideration of thecharacteristics of the drier or operation employed.

According to the present invention, the calcining of the dried mixtureof the above-described zinc compound and antimony oxide or the mixtureof the above-described zinc compound and dried antimony oxide sol orcolloidal diantimony trioxide is conducted within a temperature range offrom 500 to 1,100° C., preferably in a range of from 500 to 900° C., for30 minutes to 50 hours or preferably for 2 to 20 hours. This calciningprovides the particles of the present invention by means of a solidphase reaction.

The particle of the present invention becomes a white to bluish greencolor, depending on calcining conditions.

The particle obtained by the method of the present invention wasanalyzed by X-ray diffractometry. This analysis showed an X-raydiffraction peak identical to that of antimony oxide (ZnSb₂ O₆ for ASTMNo. 3-0455, and Zn(SbO₃)₂ for ASTM No. 11-214) described in ASTM (Indexto the X-ray Powder Data File Inorganic) and no X-ray diffraction peakof zinc oxide or diantimony pentoxide anhydride, determining that theparticle had the structure of ZnSb₂ O₆. However, for a calciningtemperature range of from 500 to 680° C., the X-ray diffraction peakoccurred at the lower diffraction angle side of the peak described inASTM, which suggested that the particle had an open structure. The peakdiffraction angle of the X-ray diffraction peak in the case of acalcining temperature of 680° C. or above also matched the valuedescribed in ASTM. A differential thermal analysis (DTA-TG) of theparticle of this invention confirmed that the particle showed no weightloss within a temperature range of room temperature to 1,000° C., andthat the particle had a crystal structure of zinc antimonate anhydridehaving no crystal water.

Observation of the particle of the present invention under atransmission electron microscope confirmed that the particle had aprimary particle size of from 5 to 500 nm and that the particle wascolloidal fine particle. The primary particle size specified in thisinvention means the diameter of a single particle in a non-aggregatedstate.

The inventors found a surprising fact in that the particle of thisinvention obtained by calcining within a temperature range of from 500to 680° C. show a resistivity ranging from 0.1K Ω to 1M Ω and electricconductivity by way of electron conduction.

Since the particles obtained by this invention showed a very slightsintering effect during calcining, they are easily pulverized to 2 μm orless even when they are in a aggregated state employing a dry powderingprocess such as that using a Jet-O-Mizer, a pin-disc mill, or a ballmill. Also, the particles of this invention can easily form an aqueoussol or an organic solvent sol by wet-pulverization in water or anorganic solvent using a sand grinder, a ball mill, a homogenizer, adisper, or a colloid mill. It was confirmed that the particle of thisinvention formed no zinc antimonate hydrate even when pulverized andheated in water, and that they maintained the crystal structure of zincantimonate anhydride.

When the particles of this invention are subjected to wet-pulverizationto form an organic solvent sol containing dispersed particles, the solmay be stabilized by adding, at need, an alkyl amine such as ethylamine,propylamine, isopropylamine, or diisobutylamine, an alkanolamine such astriethanolamine or monoethanolamine, a diamine such as ethylenediamine,or an hydroxy-carboxylic acid such as lactic acid, tartaric acid, malicacid, or citric acid. An alcohol such as methyl alcohol, ethyl alcohol,propyl alcohol, or butyl alcohol, a glycol such as ethyleneglycol,diethyleneglycol, or hexyleneglycol, a cellosolve such asethylcellosolve or propylcellosolve, and an amide such asdimethylformamide or dimethylacetamide may be used as an organicsolvent. The particle size in the above-described aqueous sol or organicsolvent sol is 500 nm or less.

DRAWINGS

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdescription, appended claims and accompanying drawings, wherein

FIG. 1 is a photograph of particles prepared in Example 5, taken by atransmission electron microscope with a magnification of 200,000.

FIG. 2 is an X-ray diffraction spectra of the particles prepared inExample 5.

FIG. 3 is a photograph of particles prepared in Example 6, taken by atransmission electron microscope with a magnification of 200,000.

FIG. 4 is an X-ray diffraction spectra of the particles prepared inExample 6.

DESCRIPTION

Regarding the production of the particles of the present invention, whenthe molar ratio of ZnO/Sb₂ O₅ is less than 0.8 some non-reacted antimonyoxide remains in the product mixture to form an undesirable mixture ofzinc antimonate anhydride and antimony oxide. When the molar ratio ofZnO/Sb₂ O₅ exceeds 1.2, the product becomes a mixture of zinc antimonate(ZnSb₂ O₆) and zinc antimonate (Zn₇ Sb₂ O₁₂), which is also undesirable.

According to the invention, the mixing time of zinc compound andcolloidal antimony oxide is in a range of from 6 minutes to 30 hours.Although a time of less than 6 minutes may not itself be undesirable,there is the possibility that mixing may be insufficient. Also, althougha mixing time of longer than 30 hours may be acceptable, such aproduction time is longer than required and consequently inefficient.The mixing temperature range is from 0 to 100° C., below 0° C. beingunfavorable owing to the freezing of antimony oxide sol. The temperaturerange can exceed 100° C., but when using antimony oxide sol there is alimitation on production equipment such as the need to use an autoclaveetc.

In this invention, the calcining temperature of the dried mixture ofzinc compound and antimony oxide sol, or the mixture of zinc compoundwith dried antimony oxide sol or with colloidal diantimony trioxide isin a range of from 500 to 1100° C. When the temperature is below 500°C., since a solid phase reaction does not occur and the particles of thepresent invention are not produced, this is unfavorable. When thetemperature is above 1100° C., volatilization of the diantimonypentoxide tends to occur during the calcining step, and coarse particlestend to occur by sintering, therefore this is also unfavorable.

Production of a sol as a starting material

Production Example I

2630 grams of sodium antimonate was dispersed in 12000 grams of water,and 2570 grams of 35% HCl was added to the mixture under agitation, themixture then being heated to 30° C. for 3 hours to cause the componentsto react. The yielded slurry of diantimony pentoxide gel was filtered bysuction, poured 15000 grams of a 3.5% HCl aqueous solution, and furtherpoured 54000 grams of water to rinse it. The obtained 2880 grams ofdiantimony pentoxide wet cake was dispersed in 10250 grams of water. 96grams of 85% phosphoric acid was added to the suspension, which was thenheated to 80° C. for 2 hours to perform peptizing. The resultant sol hadproperties such as a specific gravity of 1.132, a pH value of 1.75,viscosity of 2.3 c.p., Sb₂ O₅ content of 12.8 wt. %, P₂ O₅ of 0.45 wt.%, and Na₂ O of 0.02 wt. %. The particles in the sol were observed undera transmission electron microscope as having a particle size rangingfrom 10 to 20 nm, and the specific surface area thereof was determinedby BET method to be 105 m² /g.

Production Example II

1300 grams of Diantimony trioxide (produced by Mikuni Seiren Co., Ltd.)was dispersed in 5587 grams of water, and 953.7 grams of 35% hydrogenperoxide aqueous solution was added to the mixture, which was thenheated to 90 to 100° C. to cause the components to react for 2 hours toobtain diantimony pentoxide sol. The obtained sol exhibited a specificgravity of 1.198, a pH value of 1.80, viscosity of 19.5 c.p., and Sb₂ O₅content of 18.4 wt. %. The particles in the sol were observed under atransmission electron microscope as having a particle size in of from 20to 30 nm, and the specific surface area was determined by BET method tobe 55.0 m² /g.

Embodiment 1

1500 grams of water was added to dilute the 6000 grams of diantimonypentoxide sol (specific gravity of 1.132, Sb₂ O₅ content of 12.8 wt. %)prepared in Production Example I. The mixture was then heated to 85° C.Then, 276 grams of basic zinc carbonate (3ZnCO₃.4Zn(OH)₂, produced bythe Sakai Chemical Industry Co., Ltd. and containing 70 wt. % whenconverted to ZnO) was added to the mixture under agitation. The mixturewas further heated to 92° C. and agitated for 4.5 hours to prepare aslurry. The slurry contained 2.48 wt. % of ZnO and 9.87 wt. % of Sb₂ O₅and exhibited a ZnO/Sb₂ O₅ molar ratio of 1.0. The slurry was thenevaporated in a hot air circulation dryer at 150° C. to obtain a driedproduct. The dried product was analyzed by X-ray diffractometry, and itwas found that the peak thereof matched the peak of diantimony pentoxidehydrate (Sb₂ O₅ ×H₂ O). The dried product was powdered in a mortar, andthe resulted powder was calcined to 700° C. in an electric furnace for 4hours. The obtained white gray powder was analyzed by X-raydiffractometry, and it was confirmed that the peak thereof matched thepeak of zinc antimonate anhydride (ZnSb₂ O₆). The powder was powdered bya Jet-O-Mizer to obtain a fine powder having an average particle size of1.2 μm, determined by an apparatus for measuring particle sizedistribution by means of a centrifugal sedimentation method. The finepowder had a specific surface area of 10.4 m² /g, determined by BETmethod, and the particle size calculated from the specific surface areawas 89 nm. Observation by transmission electron microscope showed thatthe particles were colloidal particles having a square pillar shape witha primary particle size ranging from 50 to 150 nm.

Embodiment 2

400 grams of water was added to dilute the 1171.0 grams of diantimonypentoxide sol (specific gravity of 1.198, Sb₂ O₅ content of 18.4 wt. %)prepared in Production Example II. 77.44 grams of basic zinc carbonate(produced by the Sakai Chemical Industry Co. Ltd. and containing 70 wt.% when converted to ZnO) was added to the mixture and mixed underagitation for 3 hours at room temperature (25° C.). The slurry contained3.29 wt. % of ZnO and 13.07 wt. %, of Sb₂ O₅ and exhibited a ZnO/Sb₂ O₅molar ratio of 1.0. The slurry was then dried by a spray dryer to obtaina dry powder. The dry powder was analyzed by X-ray diffractometry, andit was found that the peak matched the peak of diantimony pentoxidehydrate (Sb₂ O₅ ×H₂ O). The dried powder was calcined at 800° C. in anelectric furnace for 12 hours. The obtained white gray powder wasanalyzed by X-ray diffractometry, and it was confirmed that the peakmatched the peak of zinc antimonate anhydride (ZnSb₂ O₆). The powder wasmilled by a pin-disc mill to obtain a fine powder having an averageparticle size of 1.5 μm, determined by an apparatus for measuringparticle size distribution by means of a centrifugal sedimentationmethod. The fine powder had a specific surface area of 20 m² /g,determined by BET method, and the particle size thereof calculated fromthe specific surface area was 46 nm. Observation by transmissionelectron microscope showed that the particles were colloidal particleshaving a square pillar shape and a primary particle size ranging from 30to 100 nm.

Embodiment 3

3711 grams of diantimony pentoxide sol (Sb₂ O₅ content of 18.4 wt. %)prepared in Production Example II was diluted by adding 3400 grams ofwater. 220.9 grams of basic zinc carbonate (made by Sakai ChemicalIndustry Co. Ltd. and containing 70 wt. % when converted to ZnO) wasadded to the mixture under agitation. The mixture was further heated to95° C. and agitated for 6 hours to prepare a slurry. The slurrycontained 2.11 wt. % of ZnO and 9.31 wt. % of Sb₂ O₅, and exhibited aZnO/Sb₂ O₅ molar ratio of 0.90. The slurry was then evaporated in a hotair circulation dryer at 150° C. to obtain a dried product. The driedproduct was powdered in a mortar and calcined in an electric furnace at620° C. for 12 hours to obtain a bluish green powder. The powder wasanalyzed by X-ray diffractometry, and it was found that the peak thereofmatched the peak of zinc antimonate anhydride (ZnSb₂ O₆)). The powderhad a specific surface area of 35 m² /g, determined by BET method, andthe particle size calculated from the specific surface area was 26 nm.Observation by transmission electron microscope showed that theparticles were colloidal particles having a square pillar shape and aprimary particle size ranging from 20 to 50 nm.

Embodiment 4

3711 grams of diantimony pentoxide sol (Sb₂ O₅ content of 18.4 wt. %)prepared in Production Example II was diluted by adding 3400 grams ofwater. 280.7 grams of basic zinc carbonate (produced by the SakaiChemical Industry Co., Ltd. and containing 70 wt. % when converted toZnO) was added to the mixture under agitation. The mixture was furtherheated to 95° C. and agitated for 4.5 hours to prepare a slurry, whichcontained 2.66 wt. % of ZnO and 9.24 wt. % of Sb₂ O₅ and exhibited aZnO/Sb₂ O₅ molar ratio of 1.14. The slurry was then evaporated in a hotair circulation dryer at 150° C. to obtain a dried product. The driedproduct was powdered in a mortar and fired in an electric furnace at620° C. for 12 hours to obtain a bluish green powder. The powder wasanalyzed by X-ray diffractometry, and it was found that the peak matchedthe peak of zinc antimonate anhydride (ZnSb₂ O₆)). The powder had aspecific surface area of 30 m² /g, determined by BET method, and theparticle size calculated from the specific surface area was 31 nm.Observation by transmission electron microscope showed that theparticles were colloidal particles having a square pillar shape and aprimary particle size ranging from 20 to 70 nm.

Embodiment 5

3600 grams of diantimony pentoxide sol (Sb₂ O₅ content of 18.4 wt. %)prepared in Production Example II was diluted by adding 3000 grams ofwater. 238.1 grams of basic zinc carbonate (produced by the SakaiChemical Industry Co., Ltd. and containing 70 wt. % when converted toZnO) was added to the mixture under agitation. The mixture was furtherheated to 100° C. and agitated for 11 hours to prepare a slurry, whichcontained 2.44 wt. % of ZnO and 9.69 wt. % of Sb₂ O₅ and showed aZnO/Sb₂ O₅ molar ratio of 1.0. The slurry was filtered by suction,followed by water rinsing to obtain a wet cake. The wet cake was thenevaporated in a hot air circulation dryer at 150° C. to obtain a driedproduct. The dried product was powdered in a Henschel mixer to prepare apowder, which was analyzed by X-ray diffractometry, finding that thepeak thereof matched the peak of diantimony pentoxide hydrate (Sb₂ O₅×H₂ O) and exhibited no other peaks. The obtained powder was calcined inan electric furnace at 630° C. for 13 hours to prepare a bluish greenpowder. The powder was analyzed by X-ray diffractometry, and it wasfound that the peak thereof matched the peak of zinc antimonateanhydride (ZnSb₂ O₆). The molding press-formed the powder under 100kg/cm² pressure was indicated conductivity with a specific resistivityof 100 Ωcm. The 118 grams of powder was added to 400 grams of water anddispersed with glass beads (2-3 mm in diameter) in a ball mill for 96hours, whereafter the glass beads were separated to obtain an aqueoussol of 1131.2 grams, consisting of particles having a crystallinestructure of zinc antimonate anhydride. The obtained aqueous sol wasconcentrated to 522 grams in a rotary evaporator. The obtainedconcentrated aqueous sol had a transparent bluish green color and aspecific gravity of 1.228, a pH value of 8.32, viscosity of 2.0 c.p.,conductivity of 411 μs/cm, and ZnSb₂ O₆ content of 22.6 wt. %. The solwas stable for one month at a temperature of 50° C. The sol was observedunder a transmission electron microscope (refer to FIG. 1) and exhibiteda primary particle size in a range of from 10 to 50 nm. A photometer formeasuring particle size distribution by means of a light-scatteringmethod showed the particle size to be 97.5 nm, and an apparatus formeasuring particle size sedimentation by a centrifugal sedimentationmethod measured the particle size as 70 nm. The specific surface area ofthe dried product of the sol measured by BET method was 37.6 m² /g, andthe particle size calculated from the specific surface area was 25 nm.

Embodiment 6

Diantimony pentoxide sol prepared in Production Example II was dried bya spray drier. 385.6 grams of the dried diantimony pentoxide (containing90 wt. % of Sb₂ O₅) was mixed with 125.2 grams of basic zinc carbonate(produced by the Sakai Chemical Industry Co., Ltd. and containing 70 wt.% when converted to ZnO) in a V-shaped mixer for 30 minutes. The mixturehad a ZnO/Sb₂ O₅ molar ratio of 1.0. The mixture was then calcined in anelectric furnace at 700° C. for 8 hours to obtain a white powder, whichwas analyzed by X-ray diffractometry, confirming that the peak matchedthe peak of zinc antimonate anhydride (ZnSb₂ O₆). The powder was milledin a pin-disc mill to obtain a fine powder having an average particlesize of 1.2 μm (determined by an apparatus for measuring particle sizedistribution by means of centrifugal sedimentation). 150 grams of thefine powder was added to 450 grams of water and dispersed with glassbeads (2-3 mm in diameter) in a ball mill for 120 hours. Then the glassbeads were separated to obtain an aqueous sol of 1300 grams consistingof particles having a crystal structure of zinc antimonate anhydride.The obtained aqueous sol had a white color and a specific gravity of1.100, a pH value of 5.58, viscosity of 3.1 c.p. , conductivity of 1450μs/cm, and ZnSb₂ O₆ content of 11.5 wt. %. The sol was observed by atransmission electron microscope (refer to FIG. 3), confirming a primaryparticle size in a range of from 20 to 100 nm. A photometer formeasuring particle size distribution by means of a light-scatteringmethod indicated a particle size of 432 nm, and an apparatus formeasuring particle size distribution by means of a centrifugalsedimentation method indicated a particle size of 280 nm. The solexhibited a specific surface area of 25 m² /g, determined by BET method,and the particle size calculated from the specific surface area was 37nm.

Comparative Example 1

The pre-calcined powder prepared in Embodiment 2 was calcined in anelectric furnace at 450° C. for 15 hours to obtain a yellow powder. Thepowder was observed by X-ray diffractometry, confirming that the peakthereof matched the peak of diantimony pentoxide (Sb₂ O₅), and nogeneration of zinc antimonate anhydride was observed.

Comparative Example 2

The diantimony pentoxide sol (Sb₂ O₅ content of 18.4 wt. %) prepared inProduction Example II was diluted with 400 grams of water. 54.2 grams ofbasic zinc carbonate (made by the Sakai Chemical Industry Co., Ltd. andcontaining 70 wt. % when converted to ZnO) was added to the mixtureunder agitation. The mixture was agitated at 95° C. for 6 hours toprepare a slurry, which had a ZnO content of 2.33 wt. %, Sb₂ O₅ contentof 13.3 wt. %, and ZnO/Sb₂ O₅ molar ratio of 0.70. The slurry wasevaporated in a hot air circulation drier at 150° C. to obtain a driedproduct. The dried product was pulverized in a mortar and calcined in anelectric furnace at 800° C. for 12 hours to obtain a white gray powder.The powder was analyzed by X-ray diffractometry, indicating peaks ofzinc antimonate anhydride (ZnSb₂ O₆) and diantimony tetroxide (Sb₂ O₄),generated by deoxidation of excess diantimony pentoxide, and confirmingthat the product is a mixture of these two compounds.

Comparative Example 3

58.8 grams of Diantimony trioxide (a commercial product of Lucette Inc.,grade white, specific surface area of 1.0 m² /g determined by BETmethod, primary particle size of 0.6 μm) was mixed with 16.3 grams ofzinc oxide (made by the Sakai Chemical Industry Co., Ltd., Zinc whiteNo. 1, specific surface area of 4.2 m² /g determined by BET method,primary particle size of 0.5 μm) in a mortar. The mixture was calcinedin an electric furnace at 700° C. for 12 hours to obtain a partlysintered white gray powder. The powder was observed by X-raydiffractometry and it was found that the peak matched the peak of zincantimonate anhydride (ZnSb₂ O₆). However, the specific surface area ofthe powder determined by BET method was 1.0 m² /g, and the primaryparticle size calculated from the specific surface area was 920 nm.

The particle of this invention is fine particle having a primaryparticle size in a range of from 5 to 500 nm, and the fine particle hasa ZnO/Sb₂ O₅ molar ratio in the range of from 0.8 to 1.2 and a crystalstructure of zinc antimonate anhydride (ZnSb₂ O₆).

The zinc antimonate anhydride of this invention functions as a flameretardant originating from diantimony pentoxide. When the zincantimonate anhydride is used with an organic halide along with an olefinresin such as polyethylene and polypropylene, styrene resin such aspolystyrene, anti-shock polystyrene, acrylonitrile-styrene resin, andacrylonitrile-butadiene-styrene resin (ABS resin), acrylic resin,polycarbonate, polyester such as polyethyleneterephthalate andpolybutyleneterpolyacetal, polyacetal, polyphenyleneoxide, polysulfone,thermoplastic resin such as polyamide, epoxy resin, phenol resin,thermosetting resin such as unsaturated polyester resin, andpolyurethane resin, or when the zinc antimonate anhydride is added tohalogen-containing vinyl resin, modacrylic fiber, or polyvinylchloridefiber, these resins become flame retardant materials.

In addition, the particle of this invention functions as a smokesuppressant originating from zinc oxide for halogen-containing resin.Since the particle of this invention has electrical conductivity, theycan be used as an antistatic agent of plastic forms and films, plasticfibers, glass, and papers. In particular, since the sol consisting ofthe particles of this invention has high transparency, it can be used asa transparent antistatic agent, a hard coat agent of high reflectiveindex, or anti-reflection agent when used along with a part-hydrolyzedliquid of silane coupling agent, hydrolyzed liquid of ethylsilicate ormethylsilicate, or mixed with a resin emulsion or ultraviolet curingresin. Since the sol has electrical conductivity, it can be used as anelectrical viscous fluid by dispersing it into silicone oil or the like.It can also be used as a ceramic resistor. The particle of thisinvention has a primary particle size in the range of from 5 to 500 nm,and in particular the sol thereof has a dispersion characteristic veryclose to individual primary particle. Accordingly, the sol can be usedas a surface treating agent for metals, particularly as a corrosioninhibitor for zinc-coating steel sheets when mixed with chromiumchromate aqueous solution, or an organic resin liquid, and as amicro-filler for oxide dispersion zinc coating. The sol is alsoapplicable as a treatment agent for papers and fibers, and as anon-flammable paint. The particle of this invention is also used as amicro-filler for composites of metals, plastics, and ceramics.

What is claimed is:
 1. A coating agent comprising:(a) a particle of zincantimonate anhydride, wherein said particle has a ZnO/Sb₂ O₅ molar ratioin a range of from 0.8 to 1.2 and has a crystal structure of zincantimonate anhydride (ZnSb₂ O₆) and wherein said particle has a primaryparticle size in a range of from 5 to 500 nm; and (b) a member selectedfrom the group consisting of a liquid of a part-hydrolyzed silanecoupling agent, a liquid of a hydrolyzed ethylsilicate, a liquid of ahydrolyzed methylsilicate, and a resin emulsion.
 2. The coating agentaccording to claim 1, wherein the coat agent is an antistatic agent, ahard coat agent of high refractive index, or an antireflective agent. 3.The coating agent according to claim 1, wherein said particle iselectroconductive.
 4. The coating agent according to claim 3, whereinsaid particle has a resistivity ranging from 0.1K Ω to 1M Ω.